1. Field of the Invention:
The present invention relates to SiC complex sintered bodies having excellent high temperature-characteristics unique to SiC itself and high toughness. The sintered bodies can be produced by pressureless sintering. The present invention also relates to a process for producing such SiC complex sintered bodies.
2. Related Art Statement
As SiC sintered bodies having a single phase, there are silicon carbide sintered bodies containing a B-C based sintering assistant (hereinafter referred to as "B-C based SiC") and silicon carbide sintered bodies containing an Al based sintering assistant (hereinafter referred to as "Al based SiC"). Although the B-C based SiC has excellent characteristics at high temperatures, its toughness is poor (K.sub.IC =2-3 MN/m.sup.3/2). On the other hand, although the Al based SiC has excellent toughness, its characteristics at high temperatures are poor.
With respect to Al based SiC, Japanese patent application Laid-open No. 60-186,468 discloses ceramic structural bodies and a process for producing the same, aiming at higher toughness. The ceramic structural bodies contain at least one kind of boride of elements in Group Va or Via of the periodic in silicon carbide. The sintered bodies are obtained by mixing elements in a specified composition, molding the mixture, and firing the molding in a temperature range from 1,900.degree. C. to 2,500.degree. C.
However, according to specific examples of ceramic structural bodies disclosed in the above Japanese patent application Laid-open No. 60-186,468, fracture toughness is improved by using W.sub.2 B or MoB.sub.2 and Al as an additive and a sintering assistant, respectively, and promoting densification by hot pressing. The reason why the firing is effected by hot pressing is that since W.sub.2 B is difficult to sinter, densification cannot be attained by pressureless sintering. When MoB.sub.2 is added to Al based SiC, densification cannot be effected by pressureless sintering either. However, sintered bodies having complicated shapes cannot be obtained by hot pressing, which has low industrial applicability from standpoint of the mass productivity and manufacturing cost.
When an Al based assistant is used, an intergranular phase having a low melting point generally remains in an SiC intergranular phase, so that strength and oxidation resistance at high temperatures are. Consequently, the thus obtained sintered bodies have fatal defects as materials for use at high temperatures.